This invention relates to a deck plank of extruded plastics material and its assembly onto a supporting structure, for example, of the general type disclosed in U.S. Pat. No. 6,301,842 which issued to the Assignee of the present invention. As disclosed in this patent, it is known to extrude deck planks from a plastics material such as polyvinylchloride (PVC) and wherein the base plank is extruded of a less expensive reground or scrap plastics material or PVC, and the top surface is formed by a thin co-extruded capstock layer of more expensive or virgin PVC. The capstock layer provides the top surface with a predetermined durable color and a top pattern surface, for example, a knurl surface with a raised diamond pattern. It has also been found desirable to provide a deck plank which is reversible and with opposite sides having different colors. For example, one side of the deck plank may be gray or off white, and the opposite side may have a color of light brown or a color and texture similar to a treated wood deck plank. It is further desirable to provide for simple and quick assembly of extruded deck planks with hidden fasteners and sometimes with a water-tight seal between adjacent planks so that rain water runs off the ends of the assembled planks.